iOS开发之topLayoutGuide和bottomLayoutGuide的使用小技巧分享

附：iOS 使用LayoutGuide 来限制控件的位置，配合Auto Layout constraints

  UIButton *button = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
  [self.view addSubview:button];
  
  [button setTranslatesAutoresizingMaskIntoConstraints: NO];

  // 得到当前视图的最低基准限制，这个是对于Auto Layout constraint来说的。
  id bottomGuide = self.bottomLayoutGuide;
  NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings (button, bottomGuide);
  [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat: @"V:[button]-20-[bottomGuide]"
                                   options: 0
                                   metrics: nil
                                    views: viewsDictionary]];
  
  [self.view layoutSubviews];